CVE-2025-21791: Linux kernel · vrf: use RCU protection in l3mdev_l3_out()
Affects Linux kernelSource GCVE Database
Not known to be exploited · CVSS 7.8 High · fixed in 4.15.0-1195.210~14.04.1 : patch Linux kernel soon.
Data as of 12 Nov 2026, 19:34 UTC
- Patch
- Available – fixed in 4.15.0-1195.210~14.04.1, 4.15.0-1187.200~16.04.1, 4.15.0-1195.210~16.04.1 +99
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:HExploitation evidence
Disclosed: evidence found.
CVE published 27 Feb 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 12 Nov 2026.
What to do
Upgrade to a fixed release listed under Affected software.
Patches and advisories
- ubuntu.com/security/notices/USN-7510-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7510-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-7511-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7511-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-7512-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7516-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7516-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-7517-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7518-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7521-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7510-3 (opens in a new tab)
- ubuntu.com/security/notices/USN-7510-4 (opens in a new tab)
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 24.04 LTSlinuxpkg:deb/ubuntu/linux?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
Ubuntu 24.04 LTSlinux-awspkg:deb/ubuntu/linux-aws?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
Ubuntu 24.04 LTSlinux-azurepkg:deb/ubuntu/linux-azure?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
Ubuntu 24.04 LTSlinux-azure-6.11pkg:deb/ubuntu/linux-azure-6.11?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
Ubuntu 24.04 LTSlinux-azure-nvidiapkg:deb/ubuntu/linux-azure-nvidia?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
Ubuntu 24.04 LTSlinux-gcppkg:deb/ubuntu/linux-gcp?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
A patch addressing this vulnerability is available and included in multiple fixed Linux kernel versions such as 4.15.0-1195.210 and related builds. Users should apply the latest kernel updates from their distribution vendors, specifically those provided by Ubuntu in USN-7510-1, and reboot their systems to activate the fixes. No additional mitigation steps are required beyond applying the official patches and rebooting.
Description
CVE-2025-21791 is a high-severity vulnerability in the Linux kernel's VRF (Virtual Routing and Forwarding) implementation. The function l3mdev_l3_out() can be called without holding RCU (Read-Copy-Update) protection, leading to a potential use-after-free (UAF) condition. This flaw affects multiple Linux kernel versions, particularly those prior to certain 4.15.x updates and specific 4.11.x and 4.13.x builds. The vulnerability has been addressed by adding proper RCU read lock and unlock pairs to prevent unsafe memory access. A patch is available and included in various fixed kernel versions. System reboot is required after applying the update to ensure the fix is active.
References
- ubuntu.com/security/CVE-2025-21791 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2025-21791 (opens in a new tab)
- git.kernel.org/linus/6d0ce46a93135d96b7fa075a94a88fe0da8e8773 (opens in a new tab)
- git.kernel.org/stable/c/022cac1c693add610ae76ede03adf4d9d5a2cf21 (opens in a new tab)
- git.kernel.org/stable/c/6d0ce46a93135d96b7fa075a94a88fe0da8e8773 (opens in a new tab)
- git.kernel.org/stable/c/7b81425b517accefd46bee854d94954f5c57e019 (opens in a new tab)
- git.kernel.org/stable/c/c40cb5c03e37552d6eff963187109e2c3f78ef6f (opens in a new tab)
- git.kernel.org/stable/c/c7574740be8ce68a57d0aece24987b9be2114c3c (opens in a new tab)
- ubuntu.com/security/notices/USN-7510-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7510-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-7511-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7511-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-7512-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7516-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7516-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-7517-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7518-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7521-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7510-3 (opens in a new tab)
- ubuntu.com/security/notices/USN-7510-4 (opens in a new tab)